There aren't too many unspoiled things anymore in the wrestling business...or too many things that the older fans can hang on to. There is no reason to end Taker's streak for anyone's sake. It's not as if Taker will be known for his many title reigns...because he has hardly any. This is Taker's legacy..let one of the last legends go out with his legacy in tact.
And to say the streak means nothing unless it used to put someone over is just ridiculous. That's like saying Flair's retirement match was pointless because it didn't put anyone over.
And seriously, who the fuck is Ted Dibiasi? The kid as done fuck all since being in WWE besides for the last two months. By the looks of it Taker doesn't have much more time left in the business...maybe 2 more Mania...and that even seems like a lot at this point. If you can make people care about Ted Dibiasi THAT much within a year than I'd say the guy is damn impressive enough not to need to end the streak to get over.
Wrestling isn't about title reigns or streaks. Just ask HBK. Wrestlers are rarely remembered for their title reigns or streaks. They are remembered for the moments they produced. Legends are remembered for the matches they participated in, win or lose. Look at Michaels, he will be most likely be remembered for 3 matches, The first ladder match, the match against Taker, and the match against Flair. He lost 2 of those. Take Austin, he will be remembered for losing to Hart and his fued with McMahon, not for how many title reigns he had.
Winning streaks and title reigns are for the sole purpose of putting wrestlers over. When a wrestler has reached a certain level, they drop belts and lose their streaks because, number one, they don't need them anymore and, number two, they can help elevate others.
Trust me, Taker losing at Mania will not damage his Legacy whatsoever. People will remember the fact that he went undefeated at Mania for 16 years, not that he lost his last match.
Flairs retirement was a bit different. Much like Mick Foley, a win over Flair wasn't going to get anyone over anymore because he had become a comedy act. It got to the point were a win over Flair meant next to nothing.
People like DiBiase because they see a lot of potential in him. Much like Orton 5 years ago. Its wouldn't be insane to say that DiBiase will be a midcarder for life. It also isn't insane to say that Dibiase could become the next Orton or Cena. Personally, I wouldn't mind a newcomer like DiBiase stepping up to take on Taker at Mania, if he is given a good push with wins over some Main eventers like HBK or HHH. People are always bitching and moaning about "new blood" and "creating new stars" Here is a chance to try it out. He may drop the ball, he may run with it. There is always risk involved when you are looking for a high return. Thats just the way the world works.